Carbonate (aka carbonate-bicarbonate) buffer was popularised by Stanley Dunn as a superior alternative to a Towbin's tris-glycine as a transfer buffer in the western blot. It seems to run hotter, but gives markedly lower background.

According to Judy Brusslan, the buffer is:

• 3 mM sodium carbonate (0.38 g in 1.2 l)
• 10 mM sodium bicarbonate (1.01 g in 1.2 l)
• 10% methanol (120 ml in 1.2 l)

It comes out at pH 9.9.

For a litre of 10x, that's 3.18g of Na2CO3, 8.4g of NaHCO3. For a litre of 100x, 31.8g of Na2CO3, 84 g of NaHCO3 - a 11.58% w/v solution, which should be soluble at any temperature above ~12 C. A 50x solution (15.9g Na2CO3, 42g NaHCO3) would be 5.79% w/v, soluble down to freezing point. Which you make will depend on the lowest temperature you anticipate your laboratory reaching!

Don't forget to add the methanol when you make up the working stock.